Rouson defeated Rep. Mia Jones of Jacksonville, 23-21, after the two deadlocked on a 22-22 vote and a second round of balloting was held. Lawmakers voted by secret ballot, so who switched sides and why remains a mystery.

As caucus leader, Rouson will be chiefly responsible for recruiting candidates and raising money in the 2014 elections, and being a forceful spokesman for his party in the 2015 and 2016 legislative sessions. Florida Democrats gained five House seats in 2012, thanks in part to President Barack Obama's strong grass roots campaign, and hope to keep the momentum going in 2014.

In the highly unlikely event that Democrats were to win a majority of seats in 2014 (a net gain of 17 seats) he would be speaker of the House.

Rouson has a commanding style that some lawmakers find overly intense, but he forged bonds with several freshman members by helping them in their campaigns. He began collecting signed pledges from fellow lawmakers in November and claimed Wednesday to have a 29-to-15 lead over Jones, which quickly evaporated.

Following a tie vote that shocked most lawmakers, Rouson sat slumped in a chair and sounded resigned to defeat.

"I'm a little disappointed that seven Democrats may have done something differently, secretly. I gave it all I had," he said.

Ten minutes later, he was declared the winner. His voice breaking, Rouson said: "In my heart, the best interest of this caucus is at stake. … This is surreal for me right now."

Rouson, 58, a lawyer, has spoken freely about his religious faith and his ability to overcome substance abuse. A onetime Republican who supported Jeb Bush for governor, he recalled in a victory speech that he was the underdog candidate to run St. Petersburg's NAACP chapter and in his first run for the House.

"I've always been the underdog and the insurgent," Rouson said.

Jones, who was favored by most members of the current House Democratic leadership, pledged to work with Rouson in fighting the Republican agenda in Tallahassee. She said she wasn't concerned about who might have abandoned her. "Our caucus has spoken," Jones said. "People change their minds. … Our strength is in us being able to stand together."